1. Field of the Invention
The present invention relates to a thin film resistor to be utilized as an electronic element, and a method of producing the same.
2. Description of the Prior Art
Thin film resistors of tantalum nitride (Ta--N) and of tantalum aluminum (Ta--Al) respectively have already been practically applied. In general, a thin film resistor is preferably required to have characteristics such as a high value of sheet resistance with high stability, which changes little over a lapse of time, and a low value of temperature coefficient of resistance (TCR). The sheet resistance is expressed as .rho./d, wherein .rho. is the value of specific resistivity and d is the thickness of the film. There is no way to enhance the sheet resistance of the thin film, apart from increasing the specific resistivity (.rho.) and/or reducing the thickness of the film (d).
With respect to the tantalum nitride film, the specific resistivity may reach approximately 250.mu..OMEGA. cm, provided that the film has a composition which provides the maximum value of specific resistivity and a minimum value of thickness while exhibiting stable characteristics.
In the case of tantalum aluminum, it is possible to provide the same value of specific resistivity as that of the critical tantalum nitride film set forth above, and it is also possible to maintain the stable characteristics even if the film thickness is reduced to a half or a quarter of the value of the film thickness of the critical tantalum nitride film mentioned above. Therefore, according to the composition of tantalum and aluminum, a higher sheet resistance than that of the tantalum nitride film can be provided, since the sheet resistance is expressed as .rho./d. A thin film with the Ta--Al composition is capable of having a sheet resistance with about four times the value of sheet resistance of the thin film with the Ta--N composition.